Natural light harvesting machines. Image: Greg Scholes |
Clean solutions to human energy demands are
essential to our future. While sunlight is the most abundant source of energy
at our disposal, we have yet to learn how to capture, transfer and store solar
energy efficiently. According to University
of Toronto chemistry
professor Greg Scholes, the answers can be found in the complex systems at work
in nature.
“Solar fuel
production often starts with the energy from light being absorbed by an
assembly of molecules,” says Scholes, the D.J. LeRoy Distinguished
Professor at U of T. “The energy is stored fleetingly as vibrating
electrons and then transferred to a suitable reactor. It is the same in
biological systems. In photosynthesis, for example, antenna complexes comprised
of chlorophyll capture sunlight and direct the energy to special proteins
called reaction centers that help make oxygen and sugars. It is like plugging
those proteins into a solar power socket.”
In an article in Nature Chemistry, Scholes and colleagues
from several other universities examine the latest research in various natural
antenna complexes. Using lessons learned from these natural phenomena, they
provide a framework for how to design light harvesting systems that will route
the flow of energy in sophisticated ways and over long distances, providing a
microscopic “energy grid” to regulate solar energy conversion.
A key challenge is
that the energy from sunlight is captured by colored molecules called dyes or
pigments, but is stored for only a billionth of a second. This leaves little
time to route the energy from pigments to molecular machinery that produces
fuel or electricity. How can we harvest sunlight and utilize its energy before
it is lost?
“This is why
natural photosynthesis is so inspiring,” says Scholes. “More than 10
million billion photons of light strike a leaf each second. Of these, almost
every red-colored photon is captured by chlorophyll pigments which feed plant
growth.”
Learning the
workings of these natural light-harvesting systems fostered a vision, proposed
by Scholes and his coauthors, to design and demonstrate molecular
“circuitry” that is 10 times smaller than the thinnest electrical
wire in computer processors. These energy circuits could control, regulate,
direct, and amplify raw solar energy which has been captured by human-made
pigments, thus preventing the loss of precious energy before it is utilized.
Last
year, Scholes led a team that showed that marine algae, a normally functioning
biological system, uses quantum mechanics in order to optimize photosynthesis,
a process essential to its survival. These and other insights from the natural
world promise to revolutionize our ability to harness the power of the sun.